Method of manufacturing a semiconductor device with multilayered channel structure

ABSTRACT

A semiconductor device includes a fin field effect transistor (FinFET). The FinFET includes a channel disposed on a fin, a gate disposed over the channel and a source and drain. The channel includes at least two pairs of a first semiconductor layer and a second semiconductor layer formed on the first semiconductor layer. The first semiconductor layer has a different lattice constant than the second semiconductor layer. A thickness of the first semiconductor layer is three to ten times a thickness of the second semiconductor layer at least in one pair.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application62/427,720 filed Nov. 29, 2016, the entire disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to method of manufacturing semiconductorintegrated circuits, and more particularly to method of manufacturingsemiconductor devices including fin field effect transistors (FinFETs),and semiconductor devices.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a finfield effect transistor (Fin FET) and the use of a metal gate structurewith a high-k (dielectric constant) material. The metal gate structureis often manufactured by using gate replacement technologies, andsources and drains are formed by using an epitaxial growth method.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1D illustrate exemplary cross sectional views of a fin fieldeffect transistor (FinFET) according to some embodiments of the presentdisclosure. FIG. 1E shows a relationship between the critical thicknessof SiGe formed on Si with respect to a Ge content.

FIGS. 2A-2C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 3A-3C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 4A-4C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 5A-5C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 6A-6C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 7A-7C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 8A-8E illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 9A-9C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 10A-10C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 11A-11C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 12A-12C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 13A-13C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 14A-14C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 15A-15C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 16A-16C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 17A-17C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 18A-18C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 19A-19C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 20A-20C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 21A-21C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 22A-22D illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 23A-23D illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 24A-24C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 25A and 25B illustrate exemplary cross sectional views of a finfield effect transistor (FinFET) according to some embodiments of thepresent disclosure.

FIGS. 26A and 26B illustrate exemplary cross sectional views of a FinFETaccording to some embodiments of the present disclosure.

FIGS. 27A and 27B illustrate exemplary cross sectional views of a FinFETaccording to some embodiments of the present disclosure.

FIGS. 28A and 28B illustrate exemplary cross sectional views of a FinFETaccording to some embodiments of the present disclosure.

FIGS. 29A and 29B illustrate exemplary cross sectional views of a FinFETaccording to some embodiments of the present disclosure.

FIGS. 30A and 30B illustrate exemplary cross sectional views of a FinFETaccording to some embodiments of the present disclosure.

FIGS. 31A-31C illustrate exemplary views of a FinFET according to otherembodiments of the present disclosure.

FIGS. 32A-32C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 33A-33C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 34A-34C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 35A-35C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

FIGS. 36A-36C illustrate one of the various process stages in asemiconductor device fabrication process according to some embodimentsof the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity. In the accompanied drawings, some layers/features may beomitted for simplification.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” Further, inthe following fabrication process, there may be one or more additionaloperations in/between the described operations, and the order ofoperations may be changed.

Silicon germanium (Si_(1-x)Ge_(x)), which hereinafter may be referred toas SiGe, has been employed as a channel material for a FinFET and istypically epitaxially formed on a Si layer. Further, based on differentlattice constants between Si and SiGe, a stress (strain) is applied tothe SiGe channel, which can increase carrier mobility. However, due to alattice mismatch between the Si layer and the SiGe layer, there is acritical thickness of the epitaxially grown SiGe without generatingdefects and/or relaxing the stress. The critical thickness decreaseswith increase of a Ge content x in SiGe. For example, when x=0.3, thecritical thickness is about 52 nm. Generally, a higher channel height isadvantageous to increase a current density. However, the higher SiGeepitaxial channel layer tends to lose the strain in the channel layer.

To maintain the stress and to increase the channel height, in thepresent disclosure, one or more beam-like channel layers made of, forexample, Si, are inserted within main channel layers made of forexample, SiGe, to maintain the channel strain maintenance and toincrease the channel height of the main channel layers.

FIGS. 1A-1D illustrate exemplary cross sectional views of a fin fieldeffect transistor (FinFET) according to some embodiments of the presentdisclosure. FIG. 1A shows an exemplary cross sectional view along thechannel direction (X direction) cutting a gate and a channel, FIG. 1Bshows an exemplary cross sectional view along the Y direction cutting afin and a source/drain region, and FIG. 1C is an enlarged view of thechannel of FIG. 1A. FIG. 1D is a cross sectional view of the channellayer along Y direction.

As shown in FIGS. 1A and 1B, a base fin structure 103 is disposed over asubstrate 101. The side walls of the base fin and the upper surface ofthe substrate are covered by a liner layer 104. Further, an isolationinsulating layer 105, which is also referred to as shallow trenchisolation (STI), is disposed over the liner layer 104. In someembodiments, the substrate 101 and the base fin structure 103 are madeof Si, the liner layer 104 is made of silicon oxide and/or SiN (siliconnitride), and the isolation insulating layer 105 is made of siliconoxide.

The FinFET further include a gate dielectric layer 139 disposed over achannel fin structure (see below), a work function adjustment layer 141and a metal gate 140 capped with a cap insulating layer 142. Thesidewall of the gate structure is covered by sidewall spacers 127 and aninterlayer dielectric (ILD) layer 165 is further disposed over sidewallspacers 127.

The channel of the FinFET includes one or more first semiconductorlayers 110 and one or more second semiconductor layers 112, alternatelystacked over the base fin structure, thereby forming a channel finstructure. The first semiconductor layer 110 has a different latticeconstant than the second semiconductor layer 112. The channel finstructure includes at least two pairs of the first semiconductor layer110 and the second semiconductor layer 112 disposed on the firstsemiconductor layer 110. In FIGS. 1A and 1C, three pairs of the firstsemiconductor layer 110 and the second semiconductor layer 112 aredisposed, while in FIGS. 31A-31C, two pairs of the first semiconductorlayer 110 and the second semiconductor layer 112 are disposed. Thenumber of the pairs can be four or more and up to, for example, ten(10).

The base fin 103 and the second semiconductor layer 112 are made of Siand the first semiconductor layer 110 is Si_(1-x)Ge_(x) (hereinafter maybe referred to as SiGe), where 0.05≤x≤0.95 in some embodiments, and incertain embodiments, 0.15≤x≤0.55. In this disclosure, when asemiconductor is referred to as Si or SiGe, they are crystalline unlessotherwise defined. The composition (e.g., Ge content) of the firstsemiconductor layers 110 may vary within one layer and/or from one layerto another.

A thickness of the first semiconductor layer 110 is greater than thethickness of the second semiconductor layer 112 in the pair in someembodiments. The thickness of the first semiconductor layer 110 isgenerally limited to such a thickness that no crystalline dislocation ordefects are generated in the layer. Such a critical thickness (SiGeformed on Si) has been calculated by, for example, Matthews andBlakeslee (J. Cryst. Growth, 27, pp. 118-125 (1974)) and People and Bean(Appl. Phys. Lett., 47, pp. 322-324 (1985)), as shown in FIG. 1E. As theGe content increases, the critical thickness decreases. For example,under the People and Bean model, when x=0.3, the critical thickness isabout 52 nm. Generally, when the SiGe thickness is below the criticalthickness, the SiGe layer does not include defects, and maintains straincaused by the lattice mismatch between Si and SiGe.

With respect to the strain, the strain may be lost or weakened by athermal process performed subsequent to the epitaxial growth of the SiGelayer. Accordingly, to maintain the strain, a practical criticalthickness becomes smaller than the critical thickness shown in FIG. 1E.For example, the practical critical thickness of SiGe formed on Si isequal to or less than 70% of the critical thickness provided by thePeople and Bean's model. The People and Bean's model can be approximatedby the equation Tc=1.23x^(−3.08). Thus, the thickness T_(SiGe) of SiGelayer can be equal to or less than 0.861x^(−3.08), where x is the Gecontent. In some embodiments, the thickness of SiGe layer satisfiesT_(Si)≤0.246x^(−3.08)≤T_(SiGe)≤0.861x^(−3.08), where T_(Si) is thethickness of the beam-like Si second semiconductor layer insertedbetween the first SiGe semiconductor layers. In other words, thethickness of the SiGe layer is about 20-70% of the critical thicknessprovided by the People and Bean's model. This model and the criticalthickness ranges can be applied to other material combinations.Similarly, the Matthews and Blakeslee model can be approximated by theequation Tc=0.97x^(−1.54). The practical critical thickness is locatedbetween the People and Bean's model and the Matthews and Blakesleemodel.

In some embodiments, the thickness of the second semiconductor layers112 is in a range from about 1 nm to about 10 nm. The thickness of thefirst semiconductor layers 110 is three to ten times the thickness ofthe second semiconductor layers 112 at least in one pair. The thicknessof the first semiconductor layer 110 is in a range of about 10 nm toabout 35 nm, where the Ge content is about 0.2≤x≤0.30, in someembodiments. In other embodiments, the thickness of the firstsemiconductor layer 110 is in a range of about 10 nm to about 30 nm,where the Ge content is about 0.25≤x≤0.35. Further, the thickness of thefirst semiconductor layer 110 is in a range of about 10 nm to about 40nm, where the Ge content is about 0.15≤x≤0.25, in certain embodiments.

In the present embodiments, after the first semiconductor layer 110(SiGe) is formed on the base fin structure (Si) with a thickness of T11,the second semiconductor layer 112 with a smaller thickness T21 as abeam-like structure is formed, and then an additional firstsemiconductor layer 110 with a thickness T12, where T11 and T12 aregreater than T21, is formed. By repeating this structure, it is possibleto increase a channel height without causing crystalline defects and/orlosing strain, thereby increasing a current density flowing through thechannel of the FinFET.

In FIG. 1C, the thicknesses T11, T12 and T13 of the first semiconductorlayers 110-1, 110-2 and 110-3 may be substantially the same ordifferent. In some embodiments, T11>T12>T13. The thicknesses T21 and T22of the second semiconductor layers 112-1 and 112-2 may be substantiallythe same or different. The thickness T23 of the uppermost secondsemiconductor layer 114 is equal to or greater than T21 and T22, and isin a range from about 5 nm to about 20 nm in some embodiments. In someembodiments, T21 and T22 are in a range from about 2 nm to about 6 nm.

The width of the first and second semiconductor layers along the Xdirection may be substantially equal to each other or different fromeach other. As shown in FIG. 1C, in some embodiments, the widths of thefirst and second semiconductor layers gradually decrease along thethickness direction (Z direction). In some embodiments, W11 x>W12 x>W13x.

The width of the first and second semiconductor layers along the Ydirection may be substantially equal to each other or different fromeach other. As shown in FIG. 1D, in some embodiments, the widths of thefirst and second semiconductor layers gradually decrease along thethickness direction (Z direction). In some embodiments, W11 y>W21 y>W12y>W22 y>W13 y>W23 y, and these widths are in a range from about 3 nm toabout 20 nm in some embodiments. The widths are measured at the centerof each layer.

As shown in FIGS. 1A and 1B, the second semiconductor layers 112 and 114protrude from the first semiconductor layers 110 and extend into thesource and the drain regions and the first semiconductor layers 110 donot substantially extend into the source and the drain region. In FIG.1A, the source/drain regions refers to the region outside the regionbelow the sidewall spacers.

The second semiconductor layers 112 and 114 in the source/drain regionsare wrapped around one or more other semiconductor layers 130, which areepitaxially formed on the second semiconductor layers 112 and 114. Insome embodiments, the semiconductor layers (epitaxial source/drainlayers) 130 are made of different material than the second semiconductorlayers. In other embodiments, the semiconductor layers 130 are made ofthe same material as the second semiconductor layers. In someembodiments, the epitaxial source/drain (S/D) layer 130 is made ofSi_(1-y)Ge_(y), where 0.1≤x≤0.9. When the second semiconductor layersare made of SiGe, the Ge content of the epitaxial S/D layer 130 isgreater than the Ge content of the second semiconductor layers. Each ofthe first semiconductor layers 110 is sandwiched by the S/D epitaxiallayers 130 in the X (channel direction) direction, while each of thesecond semiconductor layers 112, 114 is sandwiched by the S/D epitaxiallayers 130 in the Z (vertical) direction and Y direction (gatedirection).

The epitaxial S/D layer 130 is further covered by a silicide or ametal-SiGe alloy layer 162 in some embodiments.

FIGS. 2A-24C illustrate various process stages in a semiconductor devicefabrication process according to some embodiments of the presentdisclosure. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements. In FIGS.2A-24C, the “A” figures (e.g., FIGS. 1A, 2A, etc.) illustrate aperspective view, the “B” figures (e.g., FIGS. 1B, 2B, etc.) illustratea cross-sectional view along the channel direction (the X direction),and the “C” figures (e.g., FIG. 1C, 2C, etc.) illustrate across-sectional view along the gate direction (Y direction) cutting thespace between gates. It is understood that additional operations can beprovided before, during, and after processes shown by FIGS. 2A-24C, andsome of the operations described below can be replaced or eliminated,for additional embodiments of the method. The order of theoperations/processes may be interchangeable.

Referring to FIGS. 2A-2C, FIGS. 2A-2C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

As shown in FIGS. 2A-2C, stacked semiconductor layers are formed over asubstrate 101. The stacked semiconductor layers include firstsemiconductor layers 10 and second semiconductor layers 12. Theuppermost second semiconductor layer 14 has a thickness greater than theother second semiconductor layers 12 in some embodiments. In oneembodiment, substrate 101 includes a single crystalline semiconductorlayer on at least its surface portion. The substrate 101 may comprise asingle crystalline semiconductor material such as, but not limited toSi, Ge, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb andInP. In one embodiment, the substrate 101 is made of Si. In otherembodiments, at least the surface portion the substrate 101 includes Geor SiGe.

The first semiconductor layers 10 and the second semiconductor layers 12are made of materials having different lattice constants, and mayinclude one or more layers of Si, Ge, SiGe, GaAs, InSb, GaP, GaSb,InAlAs, InGaAs, GaSbP, GaAsSb and InP. The first semiconductor layers 10may have a smaller energy band gap than the second semiconductor layers12.

In some embodiments, the first semiconductor layers 10 and the secondsemiconductor layers 12 are made of Si, a Si compound, SiGe, Ge or a Gecompound. In one embodiment, the first semiconductor layers 10 areSi_(1-x)Ge_(x), where x is about 0.1≤x≤1.0. In other embodiments,0.2≤x≤0.4. The second semiconductor layers 12 are Si or Si_(1-y)Ge_(y),where x>y. In this disclosure, an “M” compound” or an “M based compound”means the majority of the compound is M.

In another embodiment, the second semiconductor layers 12 areSi_(1-y)C_(y), where 0≤y≤0.1, and the first semiconductor layers 10 areSi or Si_(1-x)Ge_(x), where 0≤x≤1.0, and the substrate 101 isSi_(1-z)Ge_(z), where x≤z.

In yet other embodiments, the first semiconductor layers 10 are made ofIn_(1-x)Ga_(x)As, where x is in a range from about 0 to about 0.8, andthe second semiconductor layer 12 is made of In_(1-y)Ga_(y)As, where x≤yand y is in a range from about 0.5 to about 1.0.

In FIGS. 2A-2C, three pairs of the first semiconductor layer 10 and thesemiconductor layer 12 are disposed on the substrate 101. However, thenumber of the pairs is not limited to three, and may be as small as 2and up to 10. In some embodiments, 2-5 pairs of the first and secondsemiconductor layers are formed. By adjusting the numbers of the pairs,a driving current of the FinFET can be adjusted.

The first semiconductor layers 10 and the second semiconductor layers 12are epitaxially formed over the substrate 10. As set forth above, thethickness of the first semiconductor layers 20 is greater than thethickness of the second semiconductor layers 12. The thickness of theuppermost second semiconductor layer 14 may be the same as, smallerthan, or larger than the thickness of the first semiconductor layers 10.

In some embodiments, the thickness of the second semiconductor layers 12is in a range from about 1 nm to about 5 nm. The thickness of the firstsemiconductor layers 10 is three to ten times the thickness of thesecond semiconductor layers 12 at least in one pair in some embodiments,and is four to eight times in other embodiments. When the firstsemiconductor is made of Si_(1-x)Ge_(x) and the substrate and the secondsemiconductor layer are made of Si, the thickness of the firstsemiconductor layers 10 is in a range of about 10 nm to about 35 nm,where the Ge content is about 0.2≤x≤0.30, in some embodiments. In otherembodiments, the thickness of the first semiconductor layers 10 is in arange of about 10 nm to about 30 nm, where the Ge content is about0.25≤x≤0.35. Further, the thickness of the first semiconductor layers 10is in a range of about 10 nm to about 40 nm, where the Ge content isabout 0.15≤x≤0.25, in certain embodiments. The thickness of each of thefirst semiconductor layers 10 and/or the thickness of each of the secondsemiconductor layers 12 may be the same, or may vary. The thickness ofthe uppermost second semiconductor layer 14 is in a range from about 5nm to about 15 nm in some embodiments.

Referring to FIGS. 3A-3C, FIGS. 3A-3C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

The stacked structure shown in FIGS. 2A-2C is patterned by usingphotolithography and etching operations to form fin structures. Tofabricate the fin structures, a mask layer is formed over the stackedlayers. In some embodiments, the mask layer includes a first mask layerand a second mask layer. The first mask layer is a pad oxide layer madeof a silicon oxide, which can be formed by a thermal oxidation, thesecond mask layer is made of a silicon nitride (SiN) formed by chemicalvapor deposition (CVD), including low pressure CVD (LPCVD) and plasmaenhanced CVD (PECVD); physical vapor deposition (PVD); atomic layerdeposition (ALD); or other suitable process, in some embodiments. Themask layer is patterned into a mask pattern by using patterningoperations including photolithography and etching.

Next, the stacked layers of the first and second semiconductor layers10, 12 and the substrate 101 are patterned by using the patterned masklayer as an etching mask, thereby the stacked layers and the substrateare formed into fin structures extending in the Y direction. Each of thefin structures includes a base fin structure 103 corresponding to thesubstrate 101, and a channel fin structure including the firstsemiconductor layers 110 corresponding to the first semiconductor layers10 and the second semiconductor layers 112 corresponding to the secondsemiconductor layer 12, as shown in FIGS. 3A-3C.

Some of the fin structures are for an n-type FET and some of the finstructures are for a p-type FET. In some embodiments, one or more dummyfin structures are formed adjacent to the fin structure(s) of an activeFinFET. The fin structures extend in the X direction, are arranged inthe Y direction and protrude in the Z direction.

The width W_(cf) of the channel fin structure at the bottom most firstsemiconductor layer 110 along the Y direction is in a range from about 5nm to about 20 nm in some embodiments, and is in a range from about 6 nmto about 10 nm in other embodiments.

After the fin structures are formed, a liner layer 104 and an isolationinsulating layer 105, both including one or more layers of insulatingmaterial is formed over the substrate and the fin structures. Theinsulating material for the liner layer 104 includes one or more ofsilicon oxide, silicon nitride and silicon oxynitride (SiON). Theinsulating material for the isolation insulating layer 105 includes oneor more of silicon oxide, silicon nitride, silicon oxynitride (SiON),SiOCN, fluorine-doped silicate glass (FSG), or a low-K dielectricmaterial, formed by LPCVD (low pressure chemical vapor deposition),plasma-CVD or flowable CVD. An anneal operation may be performed afterthe formation of the isolation insulating layer 105. Then, aplanarization operation, such as a chemical mechanical polishing (CMP)method and/or an etch-back method, is performed. Then, the isolationinsulating layer 105 is recessed to expose the channel fin structures,as shown in FIGS. 3A-3C. As shown in FIGS. 3A-3C, the upper portion ofthe base fin structures is slightly exposed (≈1-5 nm) from the isolationinsulating layer 105 in some embodiments.

Referring to FIGS. 4A-4C, FIGS. 4A-4C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

In some embodiments, an optional cap semiconductor layer 118 is formedover the channel fin structures. In some embodiments, the capsemiconductor layer 118 is made of the same material as the secondsemiconductor layers 112. The thickness of the cap semiconductor layer118 is in a range from about 0.5 nm to about 3 nm in some embodiments.

After the fin structures are formed in FIGS. 3A-3C, a dummy gatestructure including a dummy gate dielectric layer 121 and a dummy gateelectrode 123 are formed over the channel fin structure as shown inFIGS. 5A-5C. The dummy gate dielectric layer and the dummy gateelectrode will be subsequently used to define and form the source/drainregions.

The dummy gate structures are formed by first blanket depositing a dummygate dielectric layer over the fin structures. The dummy gate dielectriclayer includes one or more layers of silicon oxide, silicon nitride orsilicon oxynitride. The thickness of the dummy gate dielectric layer isin a range from about 1 nm to about 5 nm in some embodiments. A dummygate electrode layer is then blanket deposited on the dummy gatedielectric layer and over the channel fin structures, such that thechannel fin structures are fully embedded in the dummy gate electrodelayer. In some embodiments, the dummy electrode layer is a conductivematerial and may be selected from a group comprising amorphous silicon,poly silicon, amorphous germanium, poly germanium, amorphoussilicon-germanium, poly silicon-germanium, metallic nitrides, metallicsilicides, metallic oxides, and metals. The dummy electrode layer may bedeposited by PVD, CVD, sputter deposition, or other techniques known andused in the art for depositing conductive materials. Other materials,conductive and non-conductive, may be used. In one embodiment, poly-Siis used. The thickness T1 of the dummy gate electrode layer is in arange from about 100 nm to about 200 nm in some embodiments. In someembodiments, the dummy gate electrode layer is subjected to aplanarization operation.

Subsequently, a mask pattern 125 is formed over the dummy gate electrodelayer 123. The mask pattern 125 includes one or more layers of SiN andsilicon oxide in some embodiments. The mask pattern 125 may be formed bya patterning operation on one or more layers of SiN and silicon oxide.The dummy gate electrode layer is patterned into the dummy gatestructures including the dummy gate electrode 123 and the dummy gatedielectric layer 121, as shown in FIGS. 5A and 5B. The dummy gatestructures are formed over portions of the channel fin structure whichare to be channels of FinFETs. Further, by patterning the dummy gatestructure, the stacked layers of the first and second semiconductorlayers are partially exposed on opposite sides of the dummy gatestructure, as source/drain (S/D) regions. In this disclosure, a sourceand a drain are interchangeably used and the structures thereof aresubstantially the same. In FIGS. 5A-5C, three dummy gate structures areformed, but the number of the dummy gate structures is not limited.

Referring to FIGS. 6A-6C, FIGS. 6A-6C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

Subsequently, sidewall spacers 127 are formed along sidewalls of thedummy gate structures. The sidewall spacers 127 may be formed bydepositing and anisotropic etching an insulating layer deposited overthe dummy gate structures, the fin structures, and the isolationinsulating layer 105. In some embodiments, the sidewall spacers 127 areformed of silicon nitride, and may have a single-layer structure. Inalternative embodiments, the sidewall spacers 127 may have a compositestructure including a plurality of layers. For example, the sidewallspacers 127 may include a silicon oxide layer and a silicon nitridelayer over the silicon oxide layer. Other materials, such as SiO₂, SiCN,SiON, SiN, SiOCN, other low k material, or combinations thereof, mayalso be used. The thickness of the sidewall spacer 127 is in a rangefrom about 5 nm to about 40 nm in some embodiments.

After the sidewall spacers 127 are formed, the uppermost secondsemiconductor layer 114 is also etched by an amount D1 in a range fromabout 1 nm to about 5 nm, in some embodiments. If a cap semiconductorlayer 118 is used, the cap semiconductor layer 118 is also etched duringthe etching operation of the sidewall spacer etching operation.

Referring to FIGS. 7A-7C, FIGS. 7A-7C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the dummy gate structure and the sidewall spaces are formed, thefirst semiconductor layers 110 exposed at the S/D region are removed.When the first semiconductor layers 110 are Ge or SiGe and the secondsemiconductor layers 112 are Si, the first semiconductor layers 110 canbe selectively removed using a wet etchant such as, but not limited toammonium hydroxide (NH₄OH), tetramethylammonium hydroxide (TMAH),ethylenediamine pyrocatechol (EDP), a potassium hydroxide (KOH)solution, a hydrochloric acid (HCl) solution, or a hot ammonia solution.A plasma dry etching or a chemical vapor etching may also be used.

In some embodiments, the first semiconductor layers 110 are pushedtoward the inside of the channel (proximity push etching) such that theends of the first semiconductor layers 110 are located under thesidewall spacers 127 or the dummy gate electrode layer 123. The amountD_(px) of the proximity push etching is in a range from about 1 nm toabout 10 nm from the plane extending from the bottom portion of thesidewall spacer 127, in some embodiments. With this proximity pushetching, it is possible to maintain channel strain. Further, because ofthe beam-like second semiconductor layers 112 in the S/D region, it isalso possible to maintain the channel strain.

Referring to FIGS. 8A-8C, FIGS. 8A-8C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the first semiconductor layers 110 are removed, the secondsemiconductor layers 112 are exposed in the S/D regions. Then, an S/Depitaxial layer 130 is epitaxially formed on the exposed secondsemiconductor layers 112. As shown ins FIGS. 8A-8C, the S/D epitaxiallayer 130 wraps around the each of the second semiconductor layers 112.

When the second semiconductor layers 112 are made of Si, the S/Depitaxial layer 130 is made of Si_(1-x)Ge_(x), where the Ge content x isgreater than the Ge content of the first semiconductor layers 110. Insome embodiments, Ge content x of the S/D epitaxial layer 130 is in arange from about 0.4 to about 1.0.

In some embodiments, there is a gap or a space 131 between the S/Depitaxial layers 130 formed on adjacent second semiconductor layers 112,as shown in FIGS. 8D and 8E. In other embodiments, the S/D epitaxiallayers 130 merge with each other and there is no gap or space betweenthe S/D epitaxial layers 130 formed on adjacent second semiconductorlayers 112.

In other embodiments, SiC, SiCP and/or SiP are utilized as the S/Depitaxial layers 130. In the case where the channel is a compoundsemiconductor such as In_(m)Ga_(1-m)As, the doped epitaxial film may be,for example, In_(n)Ga_(1-n)As, where n is smaller than or equal to m.

Referring to FIGS. 9A-9C, FIGS. 9A-9C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the S/D epitaxial layer 130 is formed, a contact etch-stop layer(CESL) 129 is formed and then a first ILD layer 133 is formed over theS/D regions, the isolation insulating layer and between the dummy gatestructures.

The CESL 129 includes one or more layers of silicon oxide, siliconnitride and silicon oxynitride (SiON). The thickness of the CSEL 129 isin a range from about 1 nm to about 20 nm in some embodiments.

The first ILD layer 133 may include a single layer or multiple layers.In some embodiments, the first ILD layer 133 includes SiO₂, SiCN, SiOC,SiON, SiOCN, SiN or a low-k material, but other suitable dielectric filmmay be used. The first ILD layer 133 maybe formed by CVD, PECVD or ALD,FCVD, or a spin-on-glass process. A planarization process, such as a CMPprocess, may be performed to remove excess materials. By theplanarization process, the upper surface of the dummy gate electrodelayer 123 is exposed in some embodiments.

Referring to FIGS. 10A-10C, FIGS. 10A-10C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

Subsequently, the dummy gate electrode 123 and the dummy gate dielectriclayer 121 are removed, thereby forming gate spaces 135. The removalprocess may include one or more etch processes. For example in someembodiments, the removal process includes selectively etching usingeither dry or wet etching. When dry etching is used, the process gas mayinclude CF₄, CHF₃, NF₃, SF₆, Br₂, HBr, Cl₂, or combinations thereof.Diluting gases such as N₂, O₂, or Ar may optionally be used. When wetetching is used, the etching solution (etchant) may includeNH₄OH:H₂O₂:H₂O (APM), NH₂OH, KOH, HNO₃:NH₄F:H₂O, and/or the like. Thedummy gate dielectric layer may be removed using a wet etch process,such as a diluted HF acid, may be used. Other processes and materialsmay be used.

Referring to FIGS. 11A-11C, FIGS. 11A-11C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the dummy gate structure is removed, a gate dielectric layer 139is formed over the channel fin structure. In some embodiments, the gatedielectric layer 139 includes one or more high-k dielectric layers(e.g., having a dielectric constant greater than 3.9). For example, theone or more gate dielectric layers may include one or more layers of ametal oxide or a silicate of Hf, Al, Zr, combinations thereof, andmulti-layers thereof. Other suitable materials include La, Mg, Ba, Ti,Pb, Zr, in the form of metal oxides, metal alloy oxides, andcombinations thereof. Exemplary materials include MgO_(x),BaTi_(x)O_(y), BaSr_(x)Ti_(y)O_(z), PbTi_(x)O_(y), PbZr_(x)Ti_(y)O_(z),SiCN, SiON, SiN, Al₂O₃, La₂O₃, Ta₂O₃, Y₂O₃, HfO₂, ZrO₂, HfSiON,YGe_(x)O_(y), YSi_(x)O_(y) and LaAlO₃, and the like. The formationmethods of gate dielectric layer 139 include molecular-beam deposition(MBD), ALD, PVD, and the like. In some embodiments, the gate dielectriclayer 139 has a thickness of about 0.5 nm to about 5 nm. In someembodiments, the gate dielectric layer 139 is formed also on sides ofthe sidewall spacers 127.

In some embodiments, an interfacial layer (not shown) may be formed overthe channel fin structure prior to forming the gate dielectric layer139, and the gate dielectric layer 139 is formed over the interfaciallayer. The interfacial layer helps buffer the subsequently formed high-kdielectric layer from the underlying semiconductor material. In someembodiments, the interfacial layer is a chemical silicon oxide, whichmay be formed by chemical reactions. For example, a chemical siliconoxide may be formed using deionized water+ozone (DIO₃), NH₄OH+H₂O₂+H₂O(APM), or other methods. Other embodiments may utilize a differentmaterial or processes for the interfacial layer. In an embodiment, theinterfacial layer has a thickness of about 0.2 nm to about 1 nm.

After the gate dielectric layer 139 is formed, a gate electrode 140 isformed over the gate dielectric layer 139. The gate electrode 140 may bea metal selected from a group of W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC,TaCN, TaSiN, Mn, Co, Pd, Ni, Re, Jr, Ru, Pt, and Zr. In someembodiments, the gate electrode 140 includes a metal selected from agroup of TiN, WN, TaN, and Ru. Metal alloys such as Ti—Al, Ru—Ta, Ru—Zr,Pt—Ti, Co—Ni and Ni—Ta may be used and/or metal nitrides such as WN_(x),TiN_(x), MoN_(x), TaN_(x), and TaSi_(x)N_(y) may be used. In someembodiments, the gate electrode 140 has a thickness in the range ofabout 5 nm to about 100 nm. The gate electrode 140 may be formed using asuitable process such as ALD, CVD, PVD, plating, or combinationsthereof. A planarization process, such as a CMP, may be performed toremove excess materials.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers 141 (see, FIG. 1A) are disposed on the gatedielectric layer 139 before forming the gate electrode 140. The workfunction adjustment layer 141 is made of a conductive material such as asingle layer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi,TaSi or TiAlC, or a multilayer of two or more of these materials. Forthe n-channel FinFET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl,HfTi, TiSi and TaSi is used as the work function adjustment layer, andfor the p-channel FinFET, one or more of TiAlC, Al, TiAl, TaN, TaAlC,TiN, TiC and Co is used as the work function adjustment layer.

Referring to FIGS. 12A-12C, FIGS. 12A-12C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

Then, the gate electrode 140 and the work function adjustment layer arerecessed, thereby forming gate recesses 143. The depth D2 of the gaterecesses 143 is in a range from about 10 nm to about 100 nm in someembodiments. In some embodiments, when the gate electrode 140 is mainlymade of W, the gate electrode may be recessed using, for example, a dryetch process using Cl₂/O₂/BCl₃, at a temperature range of 24° C. to 150°C., and at a pressure of below 1 Torr.

Referring to FIGS. 13A-13C, FIGS. 13A-13C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

The gate recesses 143 are filled with an insulating material, therebyforming gate cap layers 142 on the recessed gate electrodes 140. Thegate cap layers 142 protect the gate electrodes 140 during subsequentprocesses. In some embodiments, the gate cap layer 142 includes SiO₂,SiCN, SiON, SiN, Al₂O₃, La₂O₃, a combination thereof, or the like, butother suitable dielectric films may be used. The gate cap layer 142 maybe formed using, for example, CVD, PVD, spin-on, or the like. Othersuitable process steps may be used. A planarization process, such as aCMP, may be performed to remove excess materials.

Referring to FIGS. 14A-14C, FIGS. 14A-14C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the gate cap layers 142 are formed, the first ILD layer 133 isremoved by using a suitable etching operation.

Referring to FIGS. 15A-15C, FIGS. 15A-15C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the first ILD layer 133 is removed, a sacrificial layer 150 isformed to fully cover the gate electrodes. The sacrificial layer 150 ismade of one or more layers of amorphous silicon, poly silicon, amorphousgermanium, poly germanium, amorphous silicon-germanium, polysilicon-germanium, metallic nitrides, metallic silicides, metallicoxides, and metals, which has a high etching selectivity (e.g., 5 ormore) with respect to silicon oxide based material and silicon nitridebased material. The sacrificial layer 150 may be deposited by PVD, CVD,sputter deposition, or other techniques known and used in the art fordepositing conductive materials.

Referring to FIGS. 16A-16C, FIGS. 16A-16C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

A hard mask layer 152 is formed on the sacrificial layer 150. The hardmask layer 152 includes one or more layers of SiO₂, SiCN, SiON, SiN,Al₂O₃, La₂O₃, or the like, but other suitable dielectric films may beused. The hard mask layer 152 may be deposited by PVD, CVD, sputterdeposition, or other techniques known and used in the art for depositingconductive materials.

Referring to FIGS. 17A-17C, FIGS. 17A-17C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

Then, the hard mask layer 152 is patterned by using photolithography andetching operations. The patterned hard mask layer 152 covers a region inwhich a S/D contact is subsequently formed.

Referring to FIGS. 18A-18C, FIGS. 18A-18C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

By using the patterned hard mask layer 152 as an etching mask, thesacrificial layer 150 is etched, thereby forming openings 153. Thesacrificial layer 150 can be etched either dry or wet etching. When dryetching is used, the process gas may include CF₄, CHF₃, NF₃, SF₆, Br₂,HBr, Cl₂, or combinations thereof. Diluting gases such as N₂, O₂, or Armay optionally be used. When wet etching is used, the etching solution(etchant) may include NH₄OH:H₂O₂:H₂O (APM), NH₂OH, KOH, HNO₃:NH₄F:H₂O,and/or the like.

Referring to FIGS. 19A-19C, FIGS. 19A-19C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the openings 153 are formed, the openings are filled with a secondILD layer 155. The second ILD layer 155 may include a single layer ormultiple layers. In some embodiments, the second ILD layer 155 includesSiO₂, SiCN, SiOC, SiON, SiOCN, SiN or a low-k material, but othersuitable dielectric film may be used. The second ILD layer 155 maybeformed by CVD, PECVD or ALD, FCVD, or a spin-on-glass process. Aplanarization process, such as a CMP process, may be performed to removeexcess materials.

Referring to FIGS. 20A-20C, FIGS. 20A-20C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the second ILD layer 155 is formed, the sacrificial layer 150 isremoved, thereby forming S/D contact openings 158. The etching operationto remove the sacrificial layer 150 substantially stops on the CESL 129.

Referring to FIGS. 21A-21C, FIGS. 21A-21C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

After the S/D contact openings 158 are formed, the CESL 129 is removedfrom the S/D epitaxial layers 130 by using a suitable etching operation.In some embodiments, the CESL 129 is not fully removed from the S/Depitaxial layers 130 when the S/D epitaxial layer (fin channel) islocated closed or on the edge of the S/D contact opening 158.

Referring to FIGS. 22A-22D, FIGS. 22A-22D illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure. FIG. 22D is an enlarged view of one finstructure of FIG. 22C.

After the S/D epitaxial layers 130 are exposed by removing the CESL 129,a metal layer 160 for silicide formation is formed on the exposed S/Depitaxial layers 130. The metal layer 160 includes one or more of Ti,Ta, Ni Co and W. The thickness of the metal layer 160 is in a range fromabout 1 nm to about 10 nm in some embodiments. In certain embodiments, acover layer made of TiN is further formed on the metal layer 160.

In certain embodiments, as shown in FIG. 22D, the metal layer 160 fullyfills the gap/space between the adjacent S/D epitaxial layers 130.Further, the metal layer 160 is also formed on the sidewall of thesecond ILD 155 and the upper surface of the isolation insulating layer105.

The metal layer 160 and the cover layer may be formed using a suitableprocess such as ALD, CVD, PVD, plating, or combinations thereof.

Referring to FIGS. 23A-23D, FIGS. 23A-23D illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure. FIG. 23D is an enlarged view of one finstructure of FIG. 23C.

By applying a heat, the metal layer 160 reacts with the S/D epitaxiallayer 130, thereby forming a silicide layer 162 to reduce R_(c) betweenthe S/D structure and a contact metal formed thereafter. In someembodiments, the silicide layer 162 has a thickness between about 0.5 nmand about 10 nm.

In some embodiments, the metal layer 160 remains on the insulatingmaterial layers, such as the second ILD layer, the isolation insulatinglayer 105, sidewall spacers 127 and/or the gate cap layer 142. Incertain embodiments, after the silicide layer 162 is formed, etchingprocess is performed to remove the excess metal layer 160.

Referring to FIGS. 24A-24C, FIGS. 24A-24C illustrate one of the variousstages for a FinFET manufacturing process according to embodiments ofthe present disclosure.

Subsequently, S/D contacts 165 are formed in the S/D contact openings158 to contact the silicide layer 162 formed on the S/D epitaxial layers130.

The S/D contacts 165 may include a single layer or a multi-layerstructure. For example, in some embodiments, the S/D contact 165includes a contact liner layer, such as a diffusion barrier layer, anadhesion layer, or the like, and a contact body formed over the contactliner layer in the contact openings 158. The contact liner layer mayinclude Ti, TiN, Ta, TaN, or the like formed by ALD, CVD, or the like.The contact body may be formed by depositing a conductive material, suchas one or more layers of Ni, Ta, TaN, W, Co, Ti, TiN, Al, Cu, Au, alloysthereof, combinations thereof, or the like, but other suitable metalsmay also be used. A planarization process, such as a CMP, may beperformed to remove excess material from a surface of the second ILDlayer 155 and the gate cap layer 142.

After forming the S/D contacts 165, further CMOS processes are performedto form various features such as additional interlayer dielectriclayers, contacts/vias, interconnect metal layers, and passivationlayers, etc.

FIGS. 25A-30B illustrate exemplary cross sectional views of the S/Dregions of a fin field effect transistor (FinFET) according to someembodiments of the present disclosure.

In FIGS. 25A and 25B, after the S/D epitaxial layers 130 are formed,there is a gap/space between the adjacent S/D epitaxial layers. When themetal layer 160 is formed, the metal layer 160 fills the gap. After thesilicide layer 162 is formed, part of the S/D epitaxial layers remainsand there is an unreacted metal layer 160 on the silicide layer 162 andin the gap.

In FIGS. 26A and 26B, after the S/D epitaxial layers 130 are formed,there is a gap/space between the adjacent S/D epitaxial layers. Afterthe metal layer 160 is formed, there still is the gap. After thesilicide layer 162 is formed, part of the S/D epitaxial layers remainsand substantially all metal layers 160 deposited on the S/D epitaxiallayers 130 are consumed to form the silicide layer 162. The conductivematerial for the S/D contact 165 fills the gap.

In FIGS. 27A and 27B, after the S/D epitaxial layers 130 are formed,there is a gap/space between the adjacent S/D epitaxial layers. Afterthe metal layer 160 is formed, there still is the gap. After thesilicide layer 162 is formed, part of the S/D epitaxial layers remainsand there is an unreacted metal layer 160 on the silicide layer 162 andin the gap, but there still is the gap. The conductive material for theS/D contact 165 fills the gap.

In FIGS. 28A and 28B, after the S/D epitaxial layers 130 are formed,there is a gap/space between the adjacent S/D epitaxial layers. When themetal layer 160 is formed, the metal layer 160 fills the gap. After thesilicide layer 162 is formed, no part of the S/D epitaxial layersremains and there is an unreacted metal layer 160 on the silicide layer162 and in the gap.

In FIGS. 29A and 29B, after the S/D epitaxial layers 130 are formed,there is a gap/space between the adjacent S/D epitaxial layers. Afterthe metal layer 160 is formed, there still is the gap. After thesilicide layer 162 is formed, no part of the S/D epitaxial layersremains and substantially all metal layers 160 deposited on the S/Depitaxial layers 130 are consumed to form the silicide layer 162. Theconductive material for the S/D contact 165 fills the gap.

In FIGS. 30A and 30B, after the S/D epitaxial layers 130 are formed,there is a gap/space between the adjacent S/D epitaxial layers. Afterthe metal layer 160 is formed, there still is the gap. After thesilicide layer 162 is formed, no part of the S/D epitaxial layersremains and there is an unreacted metal layer 160 on the silicide layer162 and in the gap, but there still is the gap. The conductive materialfor the S/D contact 165 fills the gap.

FIGS. 31A-31C illustrate exemplary views of a fin field effecttransistor (FinFET) according to other embodiments of the presentdisclosure. In this embodiment, the structure is substantially the sameas that of FIGS. 24A-24C, except that two pairs of the firstsemiconductor layer 110 and the second semiconductor layer 112, 114 areformed as the channel fin structure.

FIGS. 32A-36C illustrate various process stages in a semiconductordevice fabrication process according to other embodiments of the presentdisclosure.

Throughout the various views and illustrative embodiments, likereference numbers are used to designate like elements. In FIGS. 32A-36C,the “A” figures (e.g., FIGS. 32A, 33A, etc.) illustrate a perspectiveview, the “B” figures (e.g., FIGS. 32B, 33B, etc.) illustrate across-sectional view along the gate direction (Y direction) cutting thespace between gates, and the “C” figures (e.g., FIG. 32C, 33C, etc.)illustrate a cross-sectional view along the channel direction (the Xdirection). It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 32A-36C, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable. Material, configuration,dimensions and/or processes the same as or similar to the foregoingembodiments described with respect to FIGS. 2A-24C may be employed inthe following embodiments, and detailed explanation thereof may beomitted.

Referring to FIGS. 32A-32C, after the structure shown in FIGS. 13A-13C,a mask layer 201 is formed over the first ILD layer 133 and the gatestructures. The mask layer 201 includes one or more layers of SiO₂,SiCN, SiON, SiN, Al₂O₃, La₂O₃, or the like, but other suitabledielectric films may be used. The mask layer 201 may be deposited byPVD, CVD, sputter deposition, or other techniques known and used in theart for depositing conductive materials.

Referring to FIGS. 33A-33C, the mask layer 201 is patterned by using apatterning operation, and by using the patterned mask layer 201 as anetching mask, the first ILD layer 133 and the CESL 129 are etched toform openings 203, in which the S/D epitaxial layers 130 are exposed.

Referring to FIGS. 34A-34C, after the S/D epitaxial layers 130 areexposed, a metal layer 160 for silicide formation is formed on theexposed S/D epitaxial layers 130. The metal layer 160 includes one ormore of Ti, Ta, Ni Co and W. The thickness of the metal layer 160 is ina range from about 1 nm to about 10 nm in some embodiments. In certainembodiments, a cover layer made of TiN is further formed on the metallayer 160. In certain embodiments, the metal layer 160 is also formed onthe sidewall of the first ILD 133 and the upper surface of the isolationinsulating layer 105. The metal layer 160 and the cover layer may beformed using a suitable process such as ALD, CVD, PVD, plating, orcombinations thereof.

Referring to FIGS. 35A-35C, by applying a heat, the metal layer 160reacts with the S/D epitaxial layer 130, thereby forming a silicidelayer 162. In some embodiments, the silicide layer 162 has a thicknessbetween about 0.5 nm and about 10 nm.

In some embodiments, the metal layer 160 remains on the insulatingmaterial layers, such as the first ILD layer, the isolation insulatinglayer 105, sidewall spacers 127 and/or the gate cap layer 142. Incertain embodiments, after the silicide layer 162 is formed, etchingprocess is performed to remove the excess metal layer 160.

Referring to FIGS. 36A-36C, subsequently, S/D contacts 165 are formed inthe S/D contact openings 203 to contact the silicide layer 162 formed onthe S/D epitaxial layers 130.

The S/D contacts 165 may include a single layer or a multi-layerstructure. For example, in some embodiments, the S/D contact 165includes a contact liner layer, such as a diffusion barrier layer, anadhesion layer, or the like, and a contact body formed over the contactliner layer in the contact openings 203. The contact liner layer mayinclude Ti, TiN, Ta, TaN, or the like formed by ALD, CVD, or the like.The contact body may be formed by depositing a conductive material, suchas one or more layers of Ni, Ta, TaN, W, Co, Ti, TiN, Al, Cu, Au, alloysthereof, combinations thereof, or the like, but other suitable metalsmay also be used. A planarization process, such as a CMP, may beperformed to remove excess material from a surface of the first ILDlayer 133 and the gate cap layer 142.

After forming the S/D contacts 165, further CMOS processes are performedto form various features such as additional interlayer dielectriclayers, contacts/vias, interconnect metal layers, and passivationlayers, etc.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

For example, in the present disclosure, beam-like channel layers (e.g.,second semiconductor layers 112, 114) are inserted within the mainchannel layers (e.g., first semiconductor layers 110) to maintain thechannel strain and to increase the channel height of the main channellayers. Accordingly, it is possible to increase a channel currentdensity and enhance a device performance. Further, since only thebeam-like channel layers (e.g., second semiconductor layers 112, 114)extend into the S/D region, as a wire shape by selectively etching themain channel layers from the S/D region, it is possible to achieve anappropriate S/D proximity push etching with keeping the channel strain,and to obtain the metal-all-around structure in the SD contact. Thismetal contact structure can enlarge the contact landing area to reducethe contact resistance.

In accordance with an aspect of the present disclosure, a semiconductordevice includes a fin field effect transistor (FinFET). The FinFETincludes a channel disposed on a fin, a gate disposed over the channel,and a source and drain. The channel includes at least two pairs of afirst semiconductor layer and a second semiconductor layer formed on thefirst semiconductor layer. The first semiconductor layer has a differentlattice constant than the second semiconductor layer. A thickness of thefirst semiconductor layer is three to ten times a thickness of thesecond semiconductor layer at least in one pair.

In accordance with another aspect of the present disclosure, asemiconductor device includes a fin field effect transistor (FinFET).The FinFET includes a channel disposed on a fin, a gate disposed overthe channel, and a source and drain. The channel includes a firstsemiconductor layer epitaxially formed on the fin, a secondsemiconductor layer epitaxially formed on the first semiconductor layer,a third semiconductor layer epitaxially formed on the secondsemiconductor layer, and a fourth semiconductor layer formed over thethird semiconductor layer. The first and third semiconductor layers aremade of a first semiconductor material. The second semiconductor layeris made of a second semiconductor material having a different latticeconstant than the first semiconductor material. The thicknesses of thefirst and third semiconductor layers are three to ten times a thicknessof the second semiconductor layer. The second semiconductor layerextends into the source and the drain and the first and thirdsemiconductor layers do not extend into the source and the drain.

In accordance with another aspect of the present disclosure, in a methodof forming a semiconductor device including fin field effect transistors(FinFETs), at least two pairs of a first semiconductor layer and asecond semiconductor layer formed on the first semiconductor layer areformed on a substrate. The two pairs of the first and secondsemiconductor layers and the substrate are patterned, thereby forming achannel fin formed by part of the first and second semiconductor layersand a base fin formed by part of the substrate. A source and a drain areformed. A gate structure is formed over a channel layer formed by a partof the channel fin. The first semiconductor layer has a differentlattice constant than the second semiconductor layer. A thickness of thefirst semiconductor layer is three to ten times a thickness of thesecond semiconductor layer at least in one pair.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device including a fin fieldeffect transistor (FinFET), the FinFET comprising: a channel disposed ona fin; a gate disposed over the channel; and a source and drain,wherein: the channel includes at least two pairs of a firstsemiconductor layer and a second semiconductor layer formed on the firstsemiconductor layer, the first semiconductor layer has a differentlattice constant than the second semiconductor layer, a thickness of thefirst semiconductor layer is three to ten times a thickness of thesecond semiconductor layer at least in one pair, and at least in onepair, the second semiconductor extends into the source and the drain andthe first semiconductor layer does not extend into the source and thedrain.
 2. The semiconductor device of claim 1, wherein the channelincludes three pairs of the first semiconductor layer and the secondsemiconductor layer formed on the first semiconductor layer.
 3. Thesemiconductor device of claim 1, wherein the second semiconductor layeris Si and the first semiconductor layer is Si_(1-x)Ge_(x), where0.1<x<0.9.
 4. The semiconductor device of claim 1, wherein the secondsemiconductor layer is Si and the first semiconductor layer isSi_(1-x)Ge_(x), where 0.2<x<0.4.
 5. The semiconductor device of claim 4,wherein the thickness of the second semiconductor layer is 1 nm to 5 nm.6. The semiconductor device of claim 5, wherein the thickness of thefirst semiconductor layer is 10 nm to 30 nm.
 7. The semiconductor deviceof claim 1, wherein a thickness of the second semiconductor layer in anupper most pair is greater than a thickness of the second semiconductorlayer in one or more remaining pairs.
 8. The semiconductor device ofclaim 1, wherein the channel has a tapered shape having a bottom widthgreater than a top width.
 9. The semiconductor device of claim 1,wherein the thickness of the first semiconductor layer in at least onepair is different from the thickness of the first semiconductor layer inone of more remaining pairs.
 10. A semiconductor device including a finfield effect transistor (FinFET), the FinFET comprising: a channeldisposed on a fin; a gate disposed over the channel; and a source anddrain, wherein: the channel includes: a first semiconductor layerepitaxially formed on the fin; a second semiconductor layer epitaxiallyformed on the first semiconductor layer; a third semiconductor layerepitaxially formed on the second semiconductor layer; and a fourthsemiconductor layer formed over the third semiconductor layer, the firstand third semiconductor layers are made of a first semiconductormaterial, the second semiconductor layer is made of a secondsemiconductor material having a different lattice constant than thefirst semiconductor material, thicknesses of the first and thirdsemiconductor layers are three to ten times a thickness of the secondsemiconductor layer, and the second semiconductor layer extends into thesource and the drain and the first and third semiconductor layers do notextend into the source and the drain.
 11. The semiconductor device ofclaim 10, wherein the fourth semiconductor layer is made of the secondsemiconductor material.
 12. The semiconductor device of claim 10,wherein a thickness of the fourth semiconductor layer is equal to orgreater than the thickness of the second semiconductor layer and smallerthan the thickness of the first and third semiconductor layers.
 13. Thesemiconductor device of claim 10, wherein the first semiconductormaterial is Si_(1-x)Ge_(x), and the second semiconductor material isSi_(1-y)Ge_(y), where 0≤y<x<1.0.
 14. The semiconductor device of claim10, wherein an epitaxial source/drain layer is formed around part of thesecond semiconductor layer, which extends into the source and the drain.15. The semiconductor device of claim 14, wherein a silicide layer isformed on the epitaxial source/drain layer.
 16. The semiconductor deviceof claim 15, further comprising a source contact contacting the source,wherein: the silicide layer wraps around the epitaxial source/drainlayer, and the source contact wraps around the silicide layer.
 17. Thesemiconductor device of claim 10, wherein: the fourth semiconductorlayer extends into the source and the drain, and epitaxial source/drainlayers are formed around part of the second semiconductor layer and partof the fourth semiconductor layer, which extend into the source and thedrain.
 18. The semiconductor device of claim 10, wherein: the channelfurther includes, between the third semiconductor layer and the fourthsemiconductor layer: a fifth semiconductor layer epitaxially formed onthe third semiconductor layer; and a sixth semiconductor layerepitaxially formed on the fifth semiconductor layer, the fourthsemiconductor layer is epitaxially formed on the sixth semiconductorlayer, and a thickness of the sixth semiconductor layer is three to tentimes the thickness of the second semiconductor layer and a thickness ofthe fifth semiconductor layer, and the fifth semiconductor layer extendsinto the source and the drain and the sixth semiconductor layer does notextend into the source and the drain.
 19. The semiconductor device ofclaim 18, wherein a width of the third semiconductor layer is smallerthan a width of the first semiconductor layer and greater than a widthof the sixth semiconductor layer, in a channel direction.
 20. Asemiconductor device including a fin field effect transistor (FinFET),the FinFET comprising: a channel disposed on a fin; a gate disposed overthe channel; and a source and drain, wherein: the channel includes atleast two pairs of a first semiconductor layer and a secondsemiconductor layer formed on the first semiconductor layer, the firstsemiconductor layer is made of a different material than the secondsemiconductor layer, a thickness of the first semiconductor layer isthree to ten times a thickness of the second semiconductor layer atleast in one pair, and a width of the first semiconductor layer in oneof the at least two pairs is different from a width of the firstsemiconductor layer in another of the at least two pairs.